Also I think it shouldn't be a straight carbon tax, but an "environmental externalities tax". I personally care far more about other forms of pollution (especially localized) than CO2; I don't think global warming is a non-issue, but it's not the #1 environmental issue. Point sources of particulates, NO2, etc. should be taxed as well as maximum emissions specified (obviously a steel mill should be allowed to emit more, and pay for it, at full production in an efficient way, than a badly adjusted oil-fired school furnace, even if the school chooses to ignore economic rationality.)
And interestingly coal plants are already being shuttered due to the low price of natural gas. All that without any taxes - just new technology.